1. Technical Field
The embodiments herein generally relate to wideband radio frequency (RF) low noise amplifiers (LNAs), and, more particularly, to wideband LNAs used in advanced RF wireless communications.
2. Description of the Related Art
The noise figure (NF) of the first amplifier stage in a RF receiver presents a significant bottleneck in the cascaded performance and is usually the main challenge in the design of wireless systems. To obtain low levels of sensitivity which is very important for high quality wireless receivers, the NF of the LNA should be minimized, preferably lower than 2-3 dB. The problem is even more severe if the receiver is a wideband receiver; i.e., it operates over a wide range of frequencies.
Most of the conventional wideband solutions utilize resistive feedback amplifiers despite their poor NF, resulting in poor system sensitivity. To achieve a low power high dynamic range wideband LNA, a common-gate amplifier topology, such as the one shown in FIG. 1, may be used. The circuit generally has good properties (i.e., low power, good linearity) but tends to achieve poor a NF in advanced complementary metal oxide semiconductors (CMOS) devices and is usually greater than 4 dB. That is, the circuit shown in FIG. 1 results in a NF=1+γ in deep submicron CMOS technology, which results in a NF greater than 4 dB.
To overcome the problem, a boosting technique for LNAs was proposed by Allstot, D. et al., “Design Considerations for CMOS Low-Noise Amplifiers,” 2004 IEEE Radio Frequency Integrated Circuits Symposium, pages 97-100, Fort Worth, Tex., Jun. 6-8, 2004, the complete disclosure of which, in its entirety, is herein incorporated by reference. However, this circuit, shown in FIG. 2, requires an extra amplifier to function properly. The negative amplifier feedback circuit shown in FIG. 2 may theoretically result in a lower NF (NF=1+(γ/(1−A))) than the NF of the circuit in FIG. 1. However, in practice, the NF will likely be heavily degraded by the inclusion of the extra amplifier in FIG. 2, which may tend to consume high power and generally still result in more than 2-3 dB of penalty on the NF. Therefore, in practice, the conventional circuit shown in FIG. 2 may not result in any significant improvement in the NF.
Another conventional solution is described by Chehrazi, S. et al., “A 6.5 GHz Wideband CMOS Low Noise Amplifier for Multi-Band Use,” Proceedings of the IEEE 2005 Custom Integrated Circuits Conference, 4 pages, San Jose, Calif., Sep. 21, 2005, the complete disclosure of which, in its entirety, is herein incorporated by reference. This solution also employs CMOS technology to achieve low levels of NF. However, the NF levels remain approximately 3-4 dB.
Generally, the disadvantage of the conventional solutions is that, in some applications, the required NF from the LNA should be less than approximately 2 dB. In other words, the performance obtained from these conventional solutions is generally not enough for high-quality RF reception. Accordingly, there remains a need for a LNA circuit capable of achieving low levels of NF, preferably on the order of approximately 2 dB or less, which can be used in wideband applications.